The overall objectives of this study are to examine the time trends and the environmental and host influences in aplastic anemia. In view of the association between aplastic anemia (AA) and acute myeloid leukemia (AML), an additional objective of the study is to compare the epidemiologic characteristics of these two disorders. In order to accomplish these objectives, the study will be divided in two phases. In Phase I, all new cases of AA and AML occurring in metropolitan Baltimore will be identified from 1960 through 1979, and incidence and death rates will be calculated. In this phase of this study, the temporal trends of AA will be generated. In Phase II, a case-control study will be conducted in which all new cases of AA occurring in metropolitan Baltimore from March 1980 through August 1982 will be compared with three groups: AML cases, and both hospital and non-hospital controls. In this phase, specific hypotheses related to the etiology of AA will be examined, including past history of chemical exposure and viral diseases. This investigation will attempt to define groups in the population who may be at a higher risk for AA, and possibly, also for AML. In addition, results may provide new leads in regard to the pathogenesis and natural history of AA, by assessing whether the occasional occurrence of AML among AA cases denotes a common epidemiologic pattern for these disorders.